Process for coating sheet metal strip



April 3, 1956 R. HODIL 2,740,729

PROCESS FOR COATING SHEET METAL STRIP Filed June 7, 1951 2 Sheets-Sheet1 April 3, 1956 R. HODIL PROCESS FOR COATING SHEET METAL STRIP 2Sheets-Sheet 2 Filed June 7, 1951 PNEyj.

United States Patent PROCESS FOR COATING SHEET METAL STRIP Ralph Hodil,Vandergrift, Pa., assignor to Granite City Steel Company, Granite City,111., a corporation of Delaware Application June 7, 1951, Serial No.230,307

4 Claims. (Cl. 117-102) having uniform coatings thereon regardless ofthe speed of travel of the material to be coated. 7

Another object of this invention is toprevent the pumping action causedby high speed rotation of cooperating rolls in a metallic bath therebyproviding a more uniform coating across the entire width of the sheetmetal strip.

Still another object is to provide a process for making improvedcoatings on sheet metal strip with more simple and inexpensiveapparatus.

A still further object of the invention is to provide a process forgalvanizing sheet metal strip at speeds inexc'ess of speeds used in theconventional galvanizing processes.

These and other objects and advantages will become apparent hereinafter.

This invention is embodied in a process which may be standard orconventional up to the point where the sheet metal strip leaves themetallic coating bath, and comprises then passing the metallic sheetmetal strip between two non-rotating or very slowly rotating rolls.

The invention further consists in the process hereinafter described andclaimed. In the accompanying drawings which form part of thisspecification and wherein like numerals refer to like parts whereverthey occur:

Fig. 1 is a schematic view of this invention embodied in a conventionalgalvanizing process,

Fig. 2 is an enlarged view of a vertical cross-section taken through themetallic coating kettle,

Fig. 3 is a perspective view of said kettle, and

Fig. 4 is a perspective view of a metal coating kettle having rollstherein which rotate very slowly.

Conventional process It is believed that this invention can best beunderstood by first briefly describing a conventional galvanizing process. The essential steps of a process commonly practiced are as follows.7

Referring now to Fig. 1, which is a diagrammatic sketch of aconventional galvanizing line embodying this invention, it will be seenthat said lineincludes a roll of sheet metal strip A which is free torotate in an uncoiler 1. The sheet metal strip A is passed through acleaning tank 2, which holds a suitable detergent, and an acid tank 3,which contains muriatic acid. The sheet metal strip A is then fed over aroll 4, through a conventional flux 5, into akettle 6 containing agalvanizing bath 7 under a roll 8, and upwardly through said bath 7.

Up to this point, that is, up to the point where the sheet metal strip Abegins its upward movement through the zinc bath 7, the conventionalprocess is the same as the new process. In the conventional process,however, exit rolls (not shown) are located in approximately the "ice psame relative position as the rolls 9 shown in the drawings. Theseconventional gear driven exit rolls are usually 7 /2 inches or more indiameter and rotate at the same peripheral speed as the sheet metalstrip A so that said strip A does not slide on the faces of the exitrolls as it passes therebetween.

In the conventional processes, the main limitation on the speed of thesheet metal strip A is that portion ofthe conventional process after thesheet metal strip A begins its upward movement through the bath 7. Thespeed ofv the sheet metal strip A is limited by the throw ofI of zinc bythe exit rolls when said rolls rotate in excess of a certain number ofrevolutions per minute, and by the fact that heavy coatings are appliedto the edges of said sheet metal strip A because of the pumping actionresulting from the rapidly rotating cooperating rolls. In some cases,the coating builds up so rapidly on the edges that insufiicient coatingmaterial is applied to the center portion of the sheet metal strip A.Furthermore, these exit rolls have a further disadvantage in that theymust be removed from the bath andreplaced periodically. In someconventional galvanizing processes, the sheet metal strip A is run at aspeed of feet per minute, although speeds nearing 250 feet per minutehave been attained. If the conventional exit rolls do not rotate, thedesign or spangle is always destroyed by the resultant wiping action.

The sheet metal strip A, after it leaves the exit rolls in the metallicbath 7, passes upwardly through a cooling tower 10, over a roll 11, andthen downwardly and over suitable-rolls 12 to a power take up reel 13.

New process The process embodying this invention overcomes all of theobjectionable features which characterize the conventional galvanizingprocess and which limit the speed of the sheet metal strip A. At thesame time, the process produces a good looking Spangled coating.

As hereinbefore stated, this new process is the same as a conventionalprocess up to the'point where the sheet metal strip A leaves thegalvanizing bath 7. In the new process, however, the sheet metal strip Ais passed through the rolls 9. The rolls 9, which not not rotate,

are preferably about 3 /2 inches or less in diameter and are madepreferably from a hardened abrasion resisting alloy which does notreadily combine with zinc. In practice, the rolls 9 should preferablyhave a diameter in the order of 3 /2 inches which means that arcuatesurfaces having a radii of curvature in the order of 1% inches will bepresented. Rolls of this type permit little or no zinc alloy build-up atthe edges of the sheet metal strip A and present hard arcuate surfaceswhich linearly contact each surface of the sheet metal strip A.

Eventually, this arcuate surface will wear flat. When this happens, anoncceptable product is produced'because the coated surface is white andnon-Spangled. To prevent this, rolls 9 may be rotated sutficiently topresent a new arcuate surface to the sheet metal strip A. If desired,-anew arcuate surface can be presented periodically manually ormechanically, or can be presented constantly by rotating the rolls 9very slowly in the same direction as the travel of the sheet metal stripA. The amount of rotation required to prevent the rolls from wearingfiat varies with the diameter and hardness of the rolls 9 and the speedof the sheet metal strip A and other factors. On some installations thisrotation might be of the order of one revolution per hour.

One way of presenting a new arcuate surface to the sheet metal strip Ais to provide the rolls 9 with polygonal necks 14, as shown in Fig. 3,which are positioned in a suitable housing comprising pivoted carriages15 and 16 which pivot along the bars 17 and 18. Pressure, symbolized bya weight 19, is applied to the carriage to force the roll 9 against onesurface of the sheet metal strip A. The other carriage 16 is providedwith an eyebolt which can be adjusted in accordance with the pressuredesired. This arrangement prevents excessive upward movement of the rearof the carriage 16. The pressure of the weight 19 on the carriage 15causes the r lls 9 to exert pressure on both sides of the sheet metalstrip A thereby preventing the passage of excess zinc. This arrangementallows for adjustment of both the weight 19 and eyebolt 20 so that thepressure on each surface of the sheet metal strip A will besubstantially the same for producing a uniform coating on both surfaces.When the presented arcuate surfaces of the rolls 9 wear fiat, the rolls9 are moved so thata new arcuate surface is presented. With thearrangement shown in Fig. 3, the rolls are lifted upwardly, rotatedslightly, and lowered.

If desired, a new arcuate surface can be presented to each surface ofthe strip A by constantly rotating said rolls 9 at a very slow rate. Onearrangement for accomplishing this is shown in Fig. 4 wherein one roll 9is rotatably mounted in a fixed carriage 2i and the other is rotatablymounted in a pivoted carriage 22, which pivots on a bar 23. Pressure,symbolized by a weight 24, is applied to said carriage 22. A motorrotates said rolls 9 very slowly through a suitable reducing gear system26.

With any of these arrangements, or their equivalents, the weight of thecoating applied per square foot of surface can be varied in the samemanner as with conventional rolls which rotate with the same peripheralspeed as the strip A travels. This can be accomplished by varying thelevel of the metallic bath in relation to the nip, or point of contact,of the non-rotating rolls 9. As hereinbefore stated, the rolls 9 arenon-rotating rolls, but may be rotated periodically or constantly at avery slow rate for the sole purpose of preventing wear at one specificpoint. As used in the specification and claims, the term non-rotating isused to cover both of these conditions. The term sheet metal strip asused herein is intended to include all continuous sheets or stripsregardless of their width.

The use of rolls 9, hereinbefore described, removes the limitation onthe speed of the sheet metal strip A. Because the rolls do not rotate,zinc is not thrown from the gears and rolls by centrifugal force, as inthe case of conventional rolls rotating at high speeds. Furthermore, amore uniform coating across the entire width of the sheet is producedbecause there is no pumping action which results from high speedrotation and which causes a build-up of the coating metal at certainpoints. This results in a more uniform product and in a considerablesaving of coating metal. Furthermore, this process eliminates thefrequent stoppages for roll changes required in the conventionalprocess, thereby resulting in improved production with less scrap andless maintenance.

What I claim is:

1. The method of producing a spangled galvanized sheet which comprises,introducing a continuous strip of the sheet material into a bath ofmolten zinc and continuously removing the strip vertically from thebath, passing the vertically progressing strip near its point ofemergence from the bath between a pair of opposed arcuate nonrotatingsurfaces having radii of curvature in the order of 1%" and which arepartially submerged in the zinc bath, maintaining the arcuate surfacesin contact with the opposite sides of the strip so that such arcuatesurfaces contact the strip along lines substantially directly oppositeeach other and which lie in a plane parallel to the surface of themolten zinc and which is at substantially right sheet which comprises,introducing a continuous strip of the sheet material into a bath ofmolten zinc and continuously removing the strip vertically from thebath, passing the vertically progressing strip near its point ofemergence from the bath between a pair of opposed nonrotating rollershaving a diameter in the order of 3 /2" and which are partiallysubmerged in the zinc bath, maintaining the rollers in contact with theopposite sides of the strip so that such rollers contact the strip alonglines substantially directly opposite each other and which lie in aplane parallel to the surface of the molten zinc and which is atsubstantially right angles to the strip, and maintaining the level ofthe molten Zinc fixed with relation to the lines of contact between therollers and the strip so as to obtain a continuously uniform coatingupon the strip.

3. The method of producing a Spangled galvanized sheet which comprises,introducing a continuous strip of the sheet material into a bath ofmolten zinc and continuously removing the strip vertically from thebath, passing the vertically progressing strip near its point ofemergence from the bath between a pair of opposed arcuate surfaceshaving radii of curvature in the order of 1%" and which are partiallysubmerged in the zinc bath, maintaining the arcuate surfaces in contactwith the opposite sides of the strip so that such arcuate surfacescontact the strip along lines substantially directly opposite each otherand which lie in a plane parallel to the surface of the molten zinc andwhich is at substantially right angles to the strip, maintaining thearcuate surfaces substantially constantly fixed but periodicallyrotating them a predetermined amount to present different portions ofthe arcuate surfaces in contact with the strip, and maintaining thelevel of the molten zinc fixed with relation to the lines of contactbetween the arcuate surfaces and the strip so as to obtain acontinuously uniform coating upon the strip.

4. The method of producing a Spangled galvanized sheet which comprises,introducing a continuous strip of the sheet material into a bath ofmolten Zinc and continuously removing the strip vertically from thebath, passing the vertically progressing strip near its point ofemergence'from the bath between a pair of opposed rollers having adiameter in the order of 3 /2 and which are partially submerged in thezinc bath, maintaining the rollers in contact with the opposite sides ofthe strip so that such rollers contact the strip along linessubstantially directly opposite each other and which lie in a planeparallel to the surface of the molten zinc and which is at substantiallyright angles to the strip, maintaining said rollers substantiallyconstantly fixed but periodically rotating them a predetermined amountto present different surface portions of the rollers in contact with thestrip, and maintaining the level of the molten zinc fixed with relationto the lines of contact between the rollers and the strip so as toobtain a continuously uniform coating upon the strip.

References Cited in the file of this patent UNITED STATES PATENTS850,548 Steele Apr. 16, 1907 2,126,578 Roemer et a1. Aug. 9, 19382,398,034 Oganowski Apr. 9, 1946 2,598,733 Warner June 3,. 1952

1. THE METHOD OF PRODUCING A SPANGLED GALVANIZED SHEET WHICH COMPRISES,INTRODUCING A CONTINUOUS STRIP OF THE SHEET MATERIAL INTO A BATH OFMOLTEN ZINC AND CONTINUOUSLY REMOVING THE STRIP VERTICALLY FROM THEBATH, PASSING THE VERTICALLY PROGRESSING STRIP NEAR ITS POINT OFEMERGENCE FROM THE BATH BETWEEN A PAIR OF OPPOSED ARCUATE NONROTATINGSURFACES HAVING RADII OF CURVATURE IN THE ORDER OF 1 3/4" AND WHICH AREPARTIALLY SUBMERGED IN THE ZINC BATH, MAINTAINING THE ARCUATE SURFACESIN CONTACT WITH THE OPPOSITE SIDES OF THE STRIP SO THAT SUCH ARCUATESURFACES CONTACT THE STRIP ALONG LINES SUBSTANTIALLY DIRECTLY OPPOSITEEACH OTHER AND WHICH LIE IN A PLANE PARALLEL TO THE SURFACE OF THEMOLTEN ZINC AND WHICH IS AT SUBSTANTIALLY RIGHT ANGLES TO THE STRIP, ANDMAINTAINING THE LEVEL OF THE MOLTEN ZINC FIXED WITH RELATION TO THELINES OF CONTACT BETWEEN THE ARCUATE SURFACES AND THE STRIP SO AS TOOBTAIN A CONTINUOUSLY UNIFORM COATING UPON THE STRIP.